Determination the velocity & discharge using floats

APPARATUS:

1) Tape

Measure

2) Stop-Watch

(cell phone often have a timer)

3) Meter stick TO Measure Depth (Tape Measures

are more Difficult to use)

4) Buoyant

objects such as orange

THEORY:

If a Flow Meter is not Available or Rough

Estimate is enough so we can use the float to measure the flow. The float can

be any light object such as pine cone or an orange or partially filled plastic

water bottle.

The basic idea is to Measure the time that it

takes a floating object to travel a specified distance downstream. We measure

the flow of stream. Flow is important because define the shape, size and

direction of the stream.

Measure the distance up to 50 feet along the

bank string the rope at the both ends.

1. Using

the total stream calculate the cross sectional area of the stream at the both

end. To find the total stream width and the average depth.

Total Width (feet)*

Average depth (feet) = area in feet.

2. Throw

The Float From Upstream Direction. Get a stop watch to record the time it takes

to reach the downstream. If the float moves too fast so record the data 75 or

100 instead of 50 feet. Repeat this process two more times for a total of three

measurements.

3. Now

in this step we will calculate the velocity the distance covered by float

divided by the average amount of time it took to covered the distance. If the distance is 50 feet and the time taken

by orange 100 seconds so get the velocity is 0.5 feet/sec.

50 feet/100sec=0.5sec.

4. Calculate

the mid-depth velocity by multiplying the surface velocity by 0.85.

0.5×0.85=0.43ft/sec.

5. Now calculate the discharge in

cubic feet per second (cfs) & multiplying the

Velocity (ft/sec) by the cross-sectional area (ft) of the stream.

0.43ft/secx10.73ft=4.62cfs.

USING A STAFF GUAGE

The staff gage is a long ruler placed

semi-permanently in a stream or lake used to measure the water depth. Stream

guage are the most common & useful measure and therefore emphasized here.

We can also place the staff guage in a lake to monitor changes in lake water

level. If a staff guage place on non-vertical place so knowing that the staff

guage reading is correct or not.

WHY USE A

STAFF GUAGE

We can use a staff guage to get the information

in an indirect way to calculate the stream flow. If we place the staff guage

near a section of stream for which you are collecting flow data, you can

identify the relationship between stream depth & stream flow. Once you got

this relationship so we can calculate flow from the stream depth without having

to take a time to make a detailed flow measurement. A staff guage having

numerically labeled divided in lines to take the measurement of water &

calculate easily the depth & stream flow.